3.1.1 Field of the Invention
The present invention relates to methods and apparatus for gas deposition. More specifically the present invention relates to devices and methods suitable for applying multiple thin film materials layers onto a moving substrate by atomic layer deposition (ALD) carried out at atmospheric pressure.
3.1.2 Description of the Related Art
Systems for coating moving substrates at atmospheric pressure using ALD coating methods are known and disclosed in U.S. Pat. No. 7,413,982 by Levy et al. entitled PROCESS FOR ATOMIC LAYER DEPOSITION and related disclosures by Levy et al. Levy et al. disclose in FIGS. 2 and 5 a gas distribution manifold having three gas inlet ports for receiving a first precursor gas, a second precursor gas and an inert gas therein. The distribution manifold is formed with an output face having a plurality of output channels with first output channels emitting the first precursor gas out therefrom, second output channels emitting the second precursor gas out therefrom and third output channels, disposed between each of first and second output channels, emitting the inert gas out therefrom. The output face is disposed opposed to a substrate coating surface and is uniformly spaced apart from the substrate coating surface by a distance D such that each output channel is separated from the coating surface by the distance D. The output channels are separated by partitions which are shared by adjacent output channels. The partitions substantially confine gas flow to channels defined by opposing partitions. Gas is delivered into each output channel is directed parallel to the substrate coating surface and is confined to flow in the output channel by the partitions and the substrate coating surface.
In operation, the distribution manifold and or substrate are moved relative to one another. The direction of relative motion is perpendicular to the direction of gas flow in the output channels. The relative motion sequentially advances each output channel over the coating surface. Thus the coating surface is first exposed to the first precursor flowing through a first output channel. During the period that the coating surface is exposed to the first precursor the first precursor reacts with the substrate coating surface to alter the coating surface and produce a reaction byproduct. The coating surface is next exposed to an inert gas flowing through an inert gas output channel. As shown in Levy et al. FIGS. 7A and 7B the inert gas channel removes unreacted first precursor and reaction byproduct from the coating surface and carries the outflow to an exhaust port. The coating surface is next exposed to the second precursor gas flowing through a second output channel. During the period that the coating surface is exposed to the second precursor the second precursor reacts with the substrate coating surface and forms a thin film solid coating thereon and produces a reaction byproduct. The coating surface is next exposed to a second inert gas flowing through an inert gas output channel which removes unreacted second precursor and reaction byproduct from the coating surface.
It is well know that mixed precursor gases readily react with each other and most surfaces that they come into contact with and that mixed precursors contaminate the surfaces by forming solid material layers thereon. When mixed precursors contaminate a substrate coating surface its physical and chemical properties can be compromised with very little visible sign that the surface is contaminated. In the case of the distribution manifold disclosed by Levy et al., mixed precursors in the inert gas channels can contaminate surfaces of the distribution manifold and other surfaces of the exhaust system, including pump valves and sensors that come into contact with the outflow. Surface contamination resulting from contact with mixed precursor usually leads to performance degradation and eventual failure.
One problem with the distribution manifold disclosed by Levy et al. is that the separation distance D between the coating surface and the output face of the distribution manifold is necessary small. In particular, Levy et al. disclose that a separation D of approximately 0.025 mm, or 25 μm is advantageous because it prevents precursor gases from flowing around channel partitions between the distribution head and the coating surface thereby preventing different precursors from mixing together, e.g. in the inert gas channels. Additionally Levy et al. discloses in FIGS. 8A and 8B that a small separation D advantageously reduces the reaction time of a precursor with the coating surface since the precursor reaches the coating surface more quickly. However Applicants have found that the small separation distance D is not practical in a typical coating application because many substrate materials being coated have, surface variations that exceed 25 μm; the separation distance recommended in Levy et al. In particular variations in substrate thickness, in the geometry of elements supporting the substrate and in the manifold itself can easily exceed 25 μm with the result that during movement of the coating surface past the distribution manifold at the desired coating velocity contact between the coating surface and the distribution manifold can easily occur resulting undesirable coating surface and substrate damage.
While Levy et al. argue that the small separation D is an improvement over the prior gas deposition system disclosed in U.S. Pat. No. 6,821,563 to Yudovsky, entitled GAS DISTRIBUTION SYSTEM FOR CYCLICAL LAYER DEPOSITION, the Yudovsky system uses a separation distance of 500 μm or more which is a more practical separation for coating moving surfaces.
Yudovsky discloses a cyclic layer deposition system in FIG. 1 that includes a sealed processing chamber maintained at less than atmospheric pressure during coating cycles. The system includes a gas distribution manifold supported inside the process chamber in a fixed position. The system includes a shuttle that supports a substrate being coated and transports the substrate past the gas distribution manifold in a liner motion. The distribution manifold includes first gas ports connected to a first precursor supply for receiving a first precursor gas therein, second precursor ports connected to a second precursor gas supply for receiving a second precursor gas therein, purge ports connected to an inert gas supply for receiving inert gas therein and vacuum ports connected to a vacuum system for removing gas from the process chamber. The gas ports are arranged with each precursor port flanked by opposing pump ports and with a purge port disposed between opposing first and second precursor ports.
Each of the gas port is separated from adjacent gas ports by partitions. The partitions extend close to the substrate coating surface and isolate gas flow from adjacent gas ports and direct gas flow toward the coating surface. Each gas port has an open end facing the coating surface such that gas exiting from gas ports impinges the coatings surface to either react with the coating surface as is the case for the precursor gases or purge precursors from the coating surface as the case for the inert gas exiting from the purge ports. A lower end of each partition is separated from the coatings surface by a separation spacing of about 500 μm or more to allow gas streams exiting from precursor ports to flow around the lower end of the partitions toward the adjacent vacuum ports.
While the gas distribution manifold disclosed by Yudovsky provides a more practical separation distance between the lower end of each partition and the coating surface Yudovsky suffers from other shortcomings. In particular, Yudovsky requires that the process chamber be sealed and the coating process be carried out in vacuum or at least below atmospheric pressure. This complicates loading and unloading of substrates which are transported between a load lock chamber and the process chamber at the beginning and end of each coating cycle and this substantially increases coating cycle times. Additionally Yudovsky requires that the substrate be moved past the distribution manifold by a reciprocating linear motion or that individual wafers be rotated past the gas distribution manifold a shown in FIGS. 3 and 5. This further increases process cycle times by requiring two linear motion directions in the case of the linear reciprocation and loading and unloading of wafers in the case of rotary motion.
There is a need in the art to coat webs or rolls or webs of substrate material with coatings that can be readily provided by existing ALD coating chemistries. Moreover it is desirable to apply such coatings at atmospheric pressure in order to avoid the high cost and complexity of coating substrates in a vacuum chamber and to avoid increased cycle times associated with loading substrates into and unloading substrates from a vacuum or sealed chamber. While Levy et al. disclose a system for ALD coating at atmospheric pressure, the system disclosed by Levy et al. requires a small separation distance (25 μm or less) between the substrate coating surface and the lower ends of the partitions used to form gas flow channels and a 25 μm, separation distance is impractical for many applications that require more variability in the separation distance. One problem is that the thickness of the some materials being coated can vary more than 25 μm. Another problem is that material stretching and position variations due to transport drive forces can cause the separation distance to vary more than 25 μm as the material is advanced past the gas distribution manifold. This is particularly problematic as web transport velocities reach 0.5 to 20 m/sec which is a velocity range enabled by systems and methods of the present invention. Accordingly there is a need in the art to provide systems and methods capable of delivering reliable coating ALD properties with a substrate to gas manifold separation distance in the range or 500 μm to 3 mm or more to accommodate variations in the separation distance due to variable material thickness and dynamic changes in separation distance due to material stretch and movement introduced by material transport mechanisms.
More generally, there is a need to increase ALD coating rates (e.g. as measured in square meters per minute). The present invention address this need by providing improved systems and method for ALD coating at atmospheric pressure thereby eliminating process chamber load and unload cycle times and pump down and purge cayle time associated with seal chambers used in conventional ALD coating systems. Additionally, the present invention increases coating rates per minute by optimizing unit cell dimensions and gas volume delivery to the substrate that provide complete saturation at desired substrate velocities.
Additionally there is a need to achieve faster saturation of substrate surfaces at increased substrate velocities. The present invention addresses this need by providing faster and more uniform process gas delivery and removal over substrate areas exposed to individual gas channels.
There is a further need to reduce the volume of chemistries used to achieve saturation of substrate surfaces being coated using ALD processes. The present invention addresses this need by reducing the volume of chemistries used during a first exposure by optimizing unit cell dimensions and gas volume delivery to the substrate according to desired substrate transport velocities and by providing an opportunity to reuse unreacted precursors by segregating and collecting dissimilar precursors removed during purge cycles. he reaction zone proximate to the substrate surface.